X-box-binding protein 1 - P17861 (XBP1_HUMAN)

 

Protein Feature View of PDB entries mapped to a UniProtKB sequence  

 
Function
Functions as a transcription factor during endoplasmic reticulum (ER) stress by regulating the unfolded protein response (UPR). Required for cardiac myogenesis and hepatogenesis during embryonic development, and the development of secretory tissues such as exocrine pancreas and salivary gland (By similarity). Involved in terminal differentiation of B lymphocytes to plasma cells and production of immunoglobulins (PubMed:11460154). Modulates the cellular response to ER stress in a PIK3R-dependent manner (PubMed:20348923). Binds to the cis-acting X box present in the promoter regions of major histocompatibility complex class II genes (PubMed:8349596). Involved in VEGF-induced endothelial cell (EC) proliferation and retinal blood vessel formation during embryonic development but also for angiogenesis in adult tissues under ischemic conditions. Functions also as a major regulator of the UPR in obesity-induced insulin resistance and type 2 diabetes for the management of obesity and diabetes prevention (By similarity). UniProt
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Subunit Structure
Isoform 2 interacts with SIRT1. Isoform 2 interacts with PIK3R1 and PIK3R2; the interactions are direct and induce translocation of XBP1 isoform 2 into the nucleus and the unfolded protein response (UPR) XBP1-dependent target genes activation in a ER stress- and/or insulin-dependent but PI3K-independent manner. Isoform 2 interacts with FOXO1; the interaction is direct and leads to FOXO1 ubiquitination and degradation via the proteasome pathway in hepatocytes (By similarity). Isoform 1 interacts with HM13 (PubMed:25239945). Isoform 1 interacts with RNF139; the interaction induces ubiquitination and degradation of isoform 1 (PubMed:25239945). Isoform 1 interacts (via luminal domain) with DERL1; the interaction obviates the need for ectodomain shedding prior HM13/SPP-mediated XBP1 isoform 1 cleavage (PubMed:25239945). Isoform 1 interacts with isoform 2; the interaction sequesters isoform 2 from the nucleus and enhances isoform 2 degradation in the cytoplasm (PubMed:16461360, PubMed:25239945). Isoform 1 interacts with HDAC3 and AKT1; the interactions occur in endothelial cell (EC) under disturbed flow (PubMed:25190803). Isoform 1 interacts with the oncoprotein FOS (PubMed:1903538). Isoform 2 interacts with ATF6; the interaction occurs in a ER stress-dependent manner and is required for DNA binding to the unfolded protein response element (UPRE) (PubMed:17765680). Isoform 2 interacts with PIK3R1; the interaction is direct and induces translocation of XBP1 isoform 2 into the nucleus and the unfolded protein response (UPR) XBP1-dependent target genes activation in a ER stress- and/or insulin-dependent but PI3K-independent manner (PubMed:20348923). UniProt
Domain
Isoform 1 and isoform 2 N-terminus domains are necessary for nuclear localization targeting. Isoform 1 C-terminus domain confers localization to the cytoplasm and is sufficient to impose rapid degradation (By similarity). Isoform 1 transmembrane signal-anchor domain is necessary for its own mRNA to be recruited to the endoplasmic reticulum (ER) which will undergo unconventional ERN1-dependent splicing in response to ER stress (PubMed:19394296, PubMed:21233347). Isoform 1 N-terminus and C-terminus regions are necessary for DNA-binding and weak transcriptional activity, respectively. Isoform 2 N-terminus and C-terminus regions are necessary for DNA-binding and strong transcriptional activity upon ER stress, respectively (PubMed:11779464, PubMed:8657566). Isoform 2 C-terminus region contains a nuclear exclusion signal (NES) at positions 186 through 208. Isoform 2 C-terminus region contains a degradation domain at positions 209 through 261 (PubMed:16461360). UniProt
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Data origin/color codes
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Data in green originates from UniProtKB  
Variation data (sourced from UniProt) shows non-genetic variation from the ExPASy   and dbSNP   websites.
Data in yellow originates from Pfam  , by interacting with the HMMER3 web site  
Data in purple originates from Phosphosite  .
Data in orange originates from the SCOP   (version 1.75) and SCOPe   (version 2.04) classifications.
Data in grey has been calculated using BioJava  . Protein disorder predictions are based on JRONN (Troshin, P. and Barton, G. J. unpublished), a Java implementation of RONN  
  • Red: potentially disorderd region
  • Blue: probably ordered region.
Hydropathy has been calculated using a sliding window of 15 residues and summing up scores from standard hydrophobicity tables.
  • Red: hydrophobic
  • Blue: hydrophilic.
Data in lilac represent the genomic exon structure projected onto the UniProt sequence.
Data in blue originates from PDB
  • Secstruc: Secondary structure projected from representative PDB entries onto the UniProt sequence.
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Validation Track

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Data in red indicates combined ranges of Homology Models from SBKB   and the Protein Model Portal  
The PDB to UniProt mapping is based on the data provided by the EBI SIFTS project. See also Velankar et al., Nucleic Acids Research 33, D262-265 (2005).
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